Manufacture of dextrose



Patented Dec. 29, 1936 Signor to International Patents Development Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application February 2, 1934, Serial No. 709,479. Renewed September 14, 1935 3Claims. (01.127-61) This invention relates to the production of a high purity crystalline dextrose, particularly anhydrous dextrose, from a starch converted dextrose solution, in accordance with the method 5 of crystallizing the solution in a vacuum pan in counter-distinction to the method ofcrystallizing in a crystallizer at atmospheric pressure.

Certain methods for producing crystalline dextrose by the crystallization in the vacuum pan are disclosed and claimed in United States patent to William B. Newkirk, No. 1,722,761, July 30, 1929, andin application for patent of William B. Newkirk, filed July 19, 1930, Serial No. 469,267 (Patented October 9, 1934 as No. 1,976,361).

The methods disclosed in the aforesaid patent and application for patent contemplate, particularly, the use of avacuum pan.constructed so that the vacuum may be readily varied to vary the temperature of the batch. One of the ob- :0 J'ects of ,the present invention is to adapt the process to a vacuum pan of the type which is intended to be operated at, and capable, possibly,- of being operated only at a relatively constant vacuum. a :5 Anotherobject of the present invention is to increase the yield of crystals from any given batch of converter liquor by decreasing the dex- 'trose content of the solution at the end of the crystallizi'ng operation. Thisimprovement may tals; second, an induction or graining stage at fwhich a body of nucleuscrystals is formed in this initial batch of solution; and third, a building up stage at which the crystallization of the dextrose out of solution is controlled so that it goes to build up the already formed crystals l5 without induction of any substantial quantity of new crystals. To, stop the induction of crystals at the end of the second stage, the aforesaid Patent 1,722,761 provides for inducing at once a relatively large charge; of fresh liquor which so decreases the super-saturation as to put a stop to the formation of new crystals without, however, preventing thetdepositing out of solution of.

dextrose on the already formed crystals. In accordance with one of the improvements of thedomsaid pending applications the formation of new crystals is prevented by a sharp rise of tem perature brought about by reducing the vacuum in thepan. In order to increase the yield of crystals, the process described in the pending application, provides for a gradual reduction in 5 temperature, by increase in the intensityof the vacuum, toward the end of the third stage of the process. This tends to lower a crystallizing supersaturation in the batch at the end of the crystallizing operation. 19 There are certain economical advantages, how-' ever, in using for this operation a vacuum pan which operates at a constant, or relatively constant vacuum, that is to say a vacuum pan which is not constructed for arbitrary adjustment of the vacuum. 4 When a vacuum pan of this sort is employed; the expedient of the aforesaid Patentl,722,76l for stopping induction at the end of the graining stage is employed. That is, a relatively large '20 amount of fresh liquor is introduced which reduces the supersaturation of the batch. To make possible the gradual reduction of temperature during thethird or building up stage, the

expedient, according to the present invention,

is used of adding the charges of fresh liquor to the pan-all of these methods contemplating graining a relatively small charge and adding fresh liquor to the'pan after the crystallization processat a rate faster than the water content of such liquor can be evaporated while still main:

taining a crystallizing supersaturation.- This gradually reduces the boiling point of the solu- 'tion and therewith its temperature.

In order to still further increase yield, the

present invention contemplates adding water instead of sugar liquor to the solution when the crystallization has been carried as far as .possible on a liquor feed and continuing the boiling; that is, when, except for the addition of the 40 water, the crystallizing operation would have been brought to completion. The substitution of water for liquor permits the continuation of crystallization giving a greater dry substance useable with a vacuum pan, operating to main;

pan operating at a constant vacuum.

The following is a description oil a preferred method of practicing the invention with the use of a constant pressure vacuum pan.

Dextrose hydrate sugar 01 about 99% purity or better, made for example in accordance with the processes described in the Newkirk Patents 1,471,347, October 23, 1923, and 1,521,830, January 6, 1925, is melted with water giving a solution of 25 to= Baum. A portion 01. this solution suiiicient to be 20% to 30% of the total, when grained, is introduced into the vacuum pan and concentrated at a vacuum of 2'? inches of mercury, a temperature from to Fahrenheit, until it reaches a gravity of 46 Baum or higher, at about which time graining will start. The boiling is continued for about thirty minutes, which under ordinary circumstances will give the proper number of nucleus crystals.

A comparatively large charge of fresh solution is then introduced into the vacuum pan, 5% or more of the, original batch of solution. This reduces the temperature to about 140-145 Fahrenheit. The boiling is continued and the rest of the solution is added in such quantities I and at such intervals as will effect a gradual increase in the water content oi. the solution.

Fahrenheit as posible, with an ultimate reduc- That is, the fresh solution is added at a rate which is faster than the rate at which the water can be evaporated at the vacuum at which the pan is designed or set to operate. This brings about a gradual reduction' of the boiling point and or. the temperature of the mass. The aim is to reduce the temperature to as near 125 tion of supersaturation to the zero point.

If this is not possible, water is added to the solution to bring about a further reduction of boiling point and-temperature and a resultant increase in yield.

It will be understood that the method as above described is merely typical and illustrative. 'It is applicants intention to cover all modifications within the scope of the appended claims.

-I claim:

1. Method of producing by ction in a vacuum pan a high purity crystalline dextrose from a starch converted dextrose solution which comprises adding water to the batch near the ,end of the crystallising operation to dilute the batch and completing the boiling with the solution thus diluted.

2'..In the method of producing by crystallisation in a vacuum pen a high purity crystalline dextrose from a starch converted dextrose solution which comprises an'induction stage during whichabodyotnucleuscrystalsisiormedand a building up stage during which dextrose is deposited from the solution upon the already formed nucleus crystals; the improvement which consists in maintaining a relatively constant vacuum during the building up stage and bringing about a gradual reduction oi. temperature, as the operation proceeds, by adding fresh solutiontothebatchatarateiasterthanthe rate'at which the water content of such solution is evaporated, so as to gradually reduce the boiling point of the solution.

3. Methodorproducingbycrystallimtimina vacuum pan a high purity crystalline dextrose from a starch converted dextrose solution which comprises maintaining a relatively constant vac- 

